Synthetic resin foils used in shrink packaging and shrink wrapping can be wound around a stack on a pallet and caused to adhere tightly to the stack by subjecting the synthetic resin foil to a blast or stream of hot gas from an appropriate apparatus generating such hot gas so as to shrink the foil.
Hot-gas generators for this purpose can comprise a housing in which a burner is disposed and which is formed with an outlet nozzle for the hot gas. Within the housing, the hot gas path may be bent at an angle to the flow direction from the burner as it flows to the outlet.
In practice, devices of this type can be formed as frames which also can be described as ring burners, the inner opening of the frame being sufficiently large that the frame can be placed around a shrink hood or the foil which can be placed upon the stack and raised and lowered to cause the material of this hood to shrink and adhere to the stack.
In this case, the nozzle is directed inwardly.
The frame surrounds the goods or, stated otherwise, when the frame is lowered over the stack covered with synthetic resin foil, the annular nozzle is trained inwardly on the stack as the device is lowered around the latter.
It is important in the shrinkage of such shrink hoods or, more generally, synthetic resin foils, that the temperature of the hot gasses flowing from the apparatus be maintained uniform and constant but that no flame be permitted to emerge from the nozzle.
This can be achieved with the approach used in the device described in Europatent EP No. 00 64 636 which describes an apparatus which has found practical utility.
In this system, the burner exhaust gas from the burner or burners, is mixed with cool air immediately in the region of the outlet nozzle. As a consequence, the temperature distribution of the hot gas over the cross section of the nozzle is not always uniform.